The present invention relates generally to foam dispensing apparatus and more particularly to improved orifice rods utilized within a foam dispensing head that is employed in a particular method of filling building blocks with an insulating foam. Specifically, the improved orifice rods selectively permit the desired flow rate of the mixed components to be maintained into a mixing chamber within the foam dispensing head to insure proper admixing of the foam at selected predetermined flow rates.
New and valuable uses for urethane and isocyanurate polymer compositions continue to be developed. Frequently, these uses require the development of suitable apparatus to store as well as dispense the desired polymer composition. Apparatus has been developed to permit the appropriate polymer compositions to be used as portable foaming devices which can be taken to the site where such foam is required. Alternately, stationary foam dispensing apparatus, such as reaction injection molding machines, have been developed which have been utilized to inject urethane or isocyanurate polymer compositions into fixed molds. In either approach, dispensing heads or guns have been designed which permit the urethane or isocyanurate polymer components to be mixed within either a gun or a mixing head to form the desired end product foam prior to the foam being dispensed.
The recent focusing of attention on energy saving techniques has created an interest in developing building blocks which may be insulated during their construction so that buildings utilizing such blocks have additional insulation in the sidewalls or foundation and are therefore more energy efficient.
One of the problems encountered in designing a system to be able to manufacture foam filled building blocks, such as concrete blocks, has been devising an economical and labor extensive way of adding the insulating material to the block. Insulated concrete blocks have been produced by either pressure fitting a preformed insulating material, usually a polystyrene, into the core area, or by the addition of loose fill insulation into the cavities in the blocks after the blocks have been put in place on the construction site. The former method of pressure fitting the polystyrene into the building block dramatically increases the labor costs and slows down the production line along which the blocks are produced. Systems employing this technique create a bottle neck on the production line. The latter technique of adding insulation is also labor intensive and is unsatisfactory because of the natural settling that tends to occur with the loose-filled insulating material over a period of time.
The adaption of existing urethane or isocyanurate polymer dispensers to a system which would economically permit concrete or other building blocks to be filled during their manufacture presents many of the problems previously encountered in the development of such dispensing equipment. However, it also presents additional problems which need to be addressed, such as the adaptation of dispensing equipment to a static position which can quickly inject the insulating foam into a great number of blocks within a very short time period without interruption.
Minimizing the amount of manual labor in a production line is highly desirable. The automation of a system to fill the blocks as they pass along a production line also requires that various conditions be automatically sensed and the desired response activation automatically occur. Typical of these is the sensing of a bank of blocks at a predetermined point along the fixed path of travel of the blocks along the production line so that the dispensing head and related apparatus may be automatically activated to inject the blocks with foam. Additionally, the large number of repetitions which will occur in the operation of the dispensing apparatus requires that the apparatus be able to function whenever a minimal mis-alignment in dispensing equipment occurs without damaging the equipment. Finally, because building blocks vary in size it is essential that foam be dispensible at preselected variable rates so that different sized blocks with insulating cavities may be filled on the same production line. It is also necessary, since the urethane or isocyanurate polymer compositions harden after a short period of time, that the dispensing equipment be essentially self-cleaning so that repeated use of the equipment, i.e. the injection of "shots" of foam into the blocks, will occur without clogging the dispensing apparatus.
The foregoing problems are solved in both the design of the apparatus and the method utilized to automatically fill the voids or cavities of the building blocks with an insulating foam utilizing a low pressure multiple flow orifice dispensing head having an improved plunger design.